Cutting a human brain. The call for debate has been prompted by a raft of studies in which scientists have made ‘brain organoids’.
Photograph: Neil Hall/Reuters

“I have never seen so many brains out of their heads before!” declares Dr Michael Hfuhruhurr, the world-renowned neurosurgeon played by Steve Martin who has a love affair with a brain in a jar in the 1983 movie, The Man with Two Brains.

Thirty five years on, the prospect of falling for a disembodied brain is still looking slim, but researchers have made such progress in growing and maintaining human brain tissue in the lab that a group of scientists, lawyers, ethicists and philosophers have called for an ethical debate about the work.

Writing in the journal Nature on Wednesday, 17 experts argue that it is time to consider what guidelines might be needed for dealing with lumps of human brain tissue, because the more complex they become the greater the chance that they gain consciousness, feel pleasure, pain and distress, and deserve rights of their own.

“It’s not an imminent issue, but the closer these models come to being like human brains, the more we potentially edge towards the ethical problems of human experimentation,” said Prof Hank Greely, director of the Center for Law and the Biosciences at Stanford University in California.

“Right now, I see no reason to be worried about consciousness in a six million neuron, half-a-centimetre-wide, hollow ball of cells, but we do need to be thinking about this,” he said.

The call for debate has been prompted by a raft of studies in which scientists have made “brain organoids”, or lumps of human brain from stem cells; grown bits of human brain in rodents; and kept slivers of human brain alive for weeks after surgeons have removed the tissue from patients. Though it does not indicate consciousness, in one case, scientists recorded a surge of electrical activity from a ball of brain and retinal cells when they shined a light on it.

The research is driven by a need to understand how the brain works and how it fails in neurological disorders and mental illness. Brain organoids have already been used to study autism spectrum disorders, schizophrenia and the unusually small brain size seen in some babies infected with Zika virus in the womb.

“This research is essential to alleviate human suffering. It would be unethical to halt the work,” said Nita Farahany, professor of law and philosophy at Duke University in North Carolina. “What we want is a discussion about how to enable responsible progress in the field.”

Farahany, Greely and their colleagues highlight a number of ethical issues that scientists should consider. One is how they would know if a lump of brain tissue in a dish ever developed consciousness. “This would be a lot simpler if we understood human consciousness, but we don’t. What we do know is that size matters and architecture matters. The difference between a mouse brain and a human brain is not the bricks it’s built from, it’s the structure that is built.” He did have some pointers though. “If there is no electrical activity, that’s fine. If it starts tap dancing and singing, you get worried,” he said.

If signs of consciousness are spotted in a brain organoid, scientists might be obliged to assign a guardian to stand up for the tissue’s rights, while special treatment may be in order for animals that display human-like cognitive skills after having human brain tissue implanted. “There is ultimately a deep question here: would it be wrong to create an animal that had some sort of human-like consciousness?” said Greely.

Further ethical dilemmas arise over experiments on brain tissue that has been removed from living patients in neurosurgery or shortly after death. For example, scientists may one day be able to read memories or other sensitive information from pieces of brain, raising major questions about privacy and consent.

“It’s important to remember this is not mad scientists doing this for kicks,” said Greely. “There are moral imperatives to do this research. We can’t go slicing and dicing living people to see how their brains work.”